1. Field of the Invention
The present invention relates to a thin film device provided with a means for electrostatic breakdown prevention.
2. Discussion of Background
The current-carrying capacities of various types of thin film elements such as semiconductor integrated circuit elements and thin film magnetic transducers are extremely small. As a result, if an electrostatic charge in the body of a worker handling a thin film element is applied to the thin film element during a manufacturing or assembly process, excess current will flow into the thin film element, which may readily cause electrostatic breakdown. Furthermore, the various characteristics of the thin film element may be altered by the excess current or a magnetic field, heat or the like caused by the excess current.
A specific explanation is now given by citing a thin film magnetic head employing a magnetoresistive film as a read element as an example. Magnetic multi-layer films constituted by laminating magnetic layers and non-magnetic layers and achieving a high degree of magnetoresistance effect have attracted much attention and have been put into practical use in thin film magnetic heads, as a means for supporting greater sensitivity and higher output of the magnetoresistive film. The most prominent examples among such magnetic multi-layer films are spin valve films that achieve a high degree of reproduction sensitivity. Examples of publications of the known art related to spin valve films include PHYSICAL REVIEW B vol. 43, page 1297, 1991, Journal of Applied Physics, vol. 69, page 4774, 1991 and Japanese Patent Publication (KOKAI) No. 358310/1992.
A spin valve film normally adopts a film structure constituted of NiFe/Cu/(NiFe or Co)/FeMn. A spin valve film, in which, while the magnetization of the magnetic layer (pinned layer) in contact with the antiferromagnetic layer (pin layer) is fixed, the magnetization of the other magnetic film (free layer) is made to rotate freely by an external magnetic field to achieve a non-parallel state for the magnetization, obtains a high degree of magnetoresistance effect.
However, the current-carrying capacity of a spin valve film is extremely small. As a result, if an electrostatic charge in the body of a worker handling a magnetic head assembly is applied to the magnetic head assembly during a manufacturing or assembly process, an excess current will flow into the spin valve film, which may readily cause electrostatic breakdown.
In addition, the magnetoresistance effect of the spin valve film is determined by the rotating angle of the direction of the magnetization of the free layer relative to the direction of the fixed magnetization of the pinned layer in contact with the antiferromagnetic layer. If an electrostatic charge is introduced to a spin valve film having such a structure, the direction of the fixed magnetization of the pinned layer is caused to change depending on the direction in which the charge travels or by a magnetic field, heat or the like caused by the traveling electric charge. If the direction of the fixed magnetization of the pinned layer is altered, the degree of the magnetoresistance effect is also altered and specific reproduction characteristics cannot be achieved.
As a means for preventing electrostatic breakdown in a thin film magnetic head, Japanese Unexamined Patent Publication No. 85422/1995 discloses a technology whereby an inductive thin film element and a magnetoresistive thin film element are shorted by a 10.sup.3 .OMEGA.cm to 10.sup.6 .OMEGA.cm substance and at least one diode is connected between a pair of terminals that are connected to the magnetoresistive film. A problem of this prior art technology arises in that, during the process of manufacturing the magnetic head, a resistive material for shorting the inductive thin film element and the magnetoresistive thin film element must be provided inside the thin film magnetic head.
In addition, Japanese Patent Publication (KOKAI) No. 141636/1995 discloses a technology wherein two terminals connected to the magnetoresistive film are shorted in a structure employing a flexible printed board as a lead conductor for the magnetoresistive film during the manufacturing and assembly work and the flexible printed board is cut off to open a shorted portion prior to the characteristics measurement process which follows the assembly work. The characteristics measurement work is conducted in a state in which the shorted portion is opened by cutting off the flexible printed board.
The problem of this prior art is that in order to prevent an electrostatic charge which may occur after the characteristics measurement process and an electrostatic breakdown that may result, the means for electrostatic breakdown prevention that has been lost must be reconstituted for the characteristics measurement. Since there is a risk of a charge being introduced during the transporting of the product from the manufacturer to the user, during the acceptance inspection conducted at the user, during the assembly into the magnetic disk device and the like, for instance, which may cause electrostatic breakdown and a resulting alteration in characteristics, the means for electrostatic breakdown that has been lost must be reconstituted for the characteristics measurement work in order to avoid such a risk.